Intracellular versus extracellular antibiotic resistance genes in the environment: Prevalence, horizontal transfer, and mitigation strategies

• Published in: Bioresource technology 2021-01, Vol.319, p.124181, Article 124181
• Main Authors: Zarei-Baygi, Ali, Smith, Adam L.
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; Conjugation; Disinfection; DNase degradation; Drug Resistance, Microbial - genetics; Genes, Bacterial; Membrane filtration; Natural transformation; Prevalence; Waste Water
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2020.124181

[Display omitted] •iARGs are more prevalent in nutrient rich environments such as manure and wastewater.•eARGs are the dominant ARG fraction in receiving aquatic environments.•Natural transformation of eARGs plays a crucial role in spread of antibiotic resistance.•iARGs and eARGs have differing responses to mitigation strategies in WWTPs. Antibiotic resistance genes (ARGs) are present as both intracellular and extracellular fractions of DNA in the environment. Due to the poor yield of extracellular DNA in conventional extraction methods, previous studies have mainly focused on intracellular ARGs (iARGs). In this review, we evaluate the prevalence/persistence and horizontal transfer of iARGs and extracellular ARGs (eARGs) in different environments, and then explore advanced mitigation strategies in wastewater treatment plants (WWTPs) for preventing the spread of antibiotic resistance in the environment. Although iARGs are the main fraction of ARGs in nutrient-rich environments, eARGs are predominant in receiving aquatic environments. In such environments, natural transformation of eARGs occurs with a comparable frequency to conjugation of iARGs. Further, eARGs can be adsorbed by soil and sediments particles, protected from DNase degradation, and consequently persist longer than iARGs. Collectively, these characteristics emphasize the crucial role of eARGs in the spread of antibiotic resistance in the environment. Fate of iARGs and eARGs through advanced treatment technologies (disinfection and membrane filtration) indicates that different mitigation strategies may be required for each ARG fraction to be significantly removed. Finally, comprehensive risk assessment is needed to evaluate/compare the effect of iARGs versus eARGs in the environment.